Microfluidic radiosynthesis of a radiolabeled compound using electrochemical trapping and release

ABSTRACT

Methods and apparatus enable radiosynthesis of radiolabeled compounds using electrochemical trapping and release. The trapping and release of radioactive isotopes all occur inside a microreactor, a vial or similar device, thus eliminating the need for azeotropic drying and several dead-end filling steps, as well as the necessity to move concentrated radioisotopes from one compartment of the chip to another. These and other features allow radioisotope enrichment to be carried out internally within a radiochemical synthesis chip, providing faster and more robust operation, as well as producing very high radiochemical labeling yields.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/950,976 filed Jul. 20, 2007, the contents of which is herebyincorporated in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates generally to microfluidic devices andrelated technologies. More specifically, the invention relates tomethods and devices for microfluidic radiosynthesis of radiolabeledcompounds.

BACKGROUND OF THE INVENTION

This section is intended to provide a background or context to theinvention that is recited in the claims. The description herein mayinclude concepts that could be pursued, but are not necessarily onesthat have been previously conceived or pursued. Therefore, unlessotherwise indicated herein, what is described in this section is notprior art to the description and claims in this application and is notadmitted to be prior art by inclusion in this section.

Microfluidic devices have been used for the preparation of a number ofradiopharmaceutical compounds. These compounds may be used in medicalimaging applications, such as Positron Emission Tomography (PET)systems, that create images based on the distribution ofpositron-emitting isotopes in the tissue of a patient. The isotopes aretypically administered to a patient by injection of probe molecules thatcomprise a positron-emitting isotope, such as fluorine-18, covalentlyattached to a molecule that is readily metabolized or localized in thebody or that chemically binds to receptor sites within the body.Microfluidic devices offer a variety of advantages over macroscopicreactors, such as reduced reagent consumption, high concentration ofreagents, high surface-to-volume ratios, and improved control over massand heat transfer. These devices are capable of processing smallquantities of molecular probes, as well as expediting chemicalprocessing that reduces the overall processing or cycle times,simplifies the chemical processing procedures, and at the same time,provides the flexibility to produce a wide range of probes, biomarkersand labeled drugs or drug analogs, inexpensively.

All known microfluidic reactors used for radiosynthesis reported to datehave relied on ion exchange columns as their source of concentratedF-18. Release of F-18 from such columns requires aqueous solutions ofK₂CO₃. With substitution reactions requiring anhydrous conditions, asolvent exchange procedure is necessary between the fluoride release andsubstitution steps. Most of the known microreactors, being of theflow-through type, perform the solvent exchange externally. Recentlyreported batch microreactors are capable of performing solventexchanges. See, for example, C.-C. Lee, G. Sui, A. Elizarov, C. J. Shu,Y.-S. Shin, A. N. Dooley, J. Huang, A. Daridon, P. Wyatt, D. Stout, O.N. Witte, H. C. Kolb, N. Satyamurthy, J. R. Heath, M. E. Phelps, S. R.Quake and H.-R. Tseng, Science, 310, 1793, 2005. However, theseprocesses have certain limitations because of the low permeability ofthe membranes to water vapor.

Recent developments have resulted in devices that are completelycompatible with radiosynthesis in all regards except for the need toperform water evaporations across a membrane. Alternatively, thesolvents can be evaporated without a membrane but with the risk offluoride loss and with requirements of additional time and hightemperatures, both of which have a negative effect on radiosynthesis.Electrochemical trapping of F-18 from cyclotron target water has beenreported followed by release into an organic solution. See, for example,Hamacher, K.; Hirschfelder, T.; Coenen, H. H. Appl. Radiat. Isot. 2002,56, 519. However, these techniques are not suitable for use inmicrofluidic devices since, for example, they are only applicable tostanding solutions, which cannot be reduced to microliter volume, andsuffer from long trapping times.

SUMMARY OF THE INVENTION

The present invention relates generally to microfluidic devices andrelated technologies. More specifically, embodiments of the presentinvention relate to trapping and release of radioactive isotopes insidea microreactor, a vial, a channel, or similar device, thus eliminatingthe need for azeotropic drying and several dead-end filling steps, aswell as the necessity to move concentrated radioisotopes from onecompartment of the device to another. In accordance with exampleembodiments of the present invention, radioisotope enrichment is carriedout internally within a radiochemical synthesis chip, allowing fasterand more robust operation. The disclosed methods and apparatus do notrequire an ion exchange column to trap the radioisotope, produce highradiochemical labeling yields, while providing significant increase inthe device operational speed and reducing material stress, which resultsin prolonged device life. Non-exclusive examples of the radiolabeledcompounds that may be prepared according to the process described hereininclude compounds selected from the group consisting of 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG), 6-[¹⁸F] fluoro-L-3,4-dihydroxyphenylalanine([¹⁸F]FDOPA), 6-[¹⁸F] fluoro-L-meta-tyrosine ([¹⁸F]FMT), 9-[4-[¹⁸F]fluoro-3-(hydroxymethyl)butyl] guanine ([¹⁸F]FHBG), 9-[(3-[¹⁸F]fluoro-1-hydroxy-2-propoxy)methyl] guanine ([¹⁸F]FHPG), 3-(2′-[¹⁸F]fluoroethyl)spiperone ([¹⁸F]FESP), 3′-deoxy-3-[¹⁸F] fluorothymidine([¹⁸F]FLT), 4-[¹⁸F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide([¹⁸F]p-MPPF), 2-(1-{6-[(2-[¹⁸F]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidine)malononitrile([¹⁸F]FDDNP), 2-[¹⁸F] fluoro-α-methyltyrosine, [¹⁸F] fluoromisonidazole([¹⁸F]FMISO) and 5-[¹⁸F] fluoro-2′-deoxyuridine ([¹⁸F]FdUrd).

One embodiment of the present invention relates to a method for thesynthesis of a radiolabeled compound comprising a radioactive isotopeusing a microfluidic device, the method comprising: introducing acomposition comprising a radioactive isotope to the microfluidic device,electrochemically trapping the radioactive isotope using an electrode,adding a composition comprising a reactant to the reactor,electrochemically releasing the radioactive isotope from the electrode,and contacting the reactant with the radioactive isotope to form theradiolabeled compound. While the various aspects of the presentapplication are applicable to any radioactive (or non-radioactive)material with dilute charged ions, in one aspect, the radioactiveisotope is F-18. In a different aspect, the reactant comprises mannosetriflate. In a particular variation, the composition comprising thereactant is mannose triflate/K₂CO₃/K222; and MeCN is used as a solvent.In a different aspect, the reactant isN-dimethoxytrityl-5′-O-dimethoxytrityl-3′-O-nosyl-thymidine (also knownas “BOC-BOC-Nosyl”) and the radiolabeled compound is FLT.

According to another aspect of present application, a step of blowing aninert gas and a heating of the reactor is performed to dry the trappedF-18 before adding the composition comprising the reactant to thereactor. In one particular variation, the inert gas is nitrogen orargon. In a different aspect, the reactor is a coin-shaped reactor in aradio-synthesis chip. In yet another aspect, the trapping and releasingis carried out by one or more electrodes. In one exemplary aspect, theelectrodes are located in or on at least one of a floor, a ceiling, anda side of the reactor or combinations thereof. In different aspect, theelectrodes are located in a channel in fluid communication with thereactor. According to another aspect, the electrodes are non-metalelectrodes. In one exemplary aspect, the electrodes are made of amaterial selected from the group consisting of a graphite, a compositegraphite, and silicon and combinations thereof. In a different aspect,the electrodes are graphite polymer electrodes. In yet another aspect,the polymer is selected from the group consisting of a DCPD, apolyethylene, and a glass. In one aspect, the electrodes are metalelectrodes while in a different aspect, the electrodes are covered witha protective coating.

According to another aspect of the present application, at least one ofthe electrochemical trapping and the releasing is carried out inaccordance with an on-chip feature. This feature is part of themicrofluidic chip but is located outside of the reaction chamber. In adifferent aspect, at least one of the electrochemical trapping and thereleasing is carried out in accordance with an in-reactor feature. Thisfeature is located inside of the reaction chamber. According to yetanother aspect, the trapping, the releasing and the radiolabeledcompound formation are carried out within the same microreactor. Inanother aspect, a radiochemical labeling yield of at least 55% isproduced. In one aspect, the yield is 55%, 65%, 75%, 85%, 95% or 99%. Ina different aspect, the radioactive isotope is released into anon-aqueous solution. In yet another aspect, the non-aqueous solution isan organic solution. In one variation, the organic solution comprises atleast one of acetonitrile, THF, dichloromethane, DMF, acetone, alcoholssuch as ethanol, methanol and t-amyl alcohol, DMSO, fluorous solvents,and mixtures thereof. In another aspect, the reaction to form theradiolabeled compound is a substitution reaction. In a different aspect,the releasing is carried out simultaneously or concurrent with thesubstitution reaction. In yet another aspect, the reactant is in asolvent. According to another aspect, the electrochemical trapping iscarried out in one or more passes, and in another aspect, theelectrochemical releasing is carried out in accordance with one or morereversals of a voltage bias.

Another embodiment of the present application relates to a method forthe synthesis of a radiolabeled compound using a microfluidictrap-release device, the method comprising introducing a compositioncomprising a radioactive isotope to the device, electrochemicallytrapping of the radioactive isotope, adding a composition comprising areactant to the device, and electrochemically releasing the radioactiveisotope into the trap-release device. In one aspect, the trap-releasedevice is a radiochemical microreactor.

Another embodiment of the present application relates to a microfluidicradiosynthesis apparatus, comprising a first electrode configured toelectrochemically trap a radioactive isotope, a chamber, and a secondelectrode configured to electrochemically release the radioactiveisotope into the chamber. In one aspect, the apparatus is furtherconfigured for preparing a radiolabeled compound by performing areaction of a reactant with the radioactive isotope. In a differentaspect, the radioactive isotope is F-18. In yet another aspect, thechamber is filled with a composition comprising a reactant. In oneaspect, the reactant comprises mannose triflate. According to adifferent aspect, the reactant isN-dimethoxytrityl-5′-O-dimethoxytrityl-3′-O-nosyl-thymidine and theradiolabeled compound is FLT. In another aspect, the apparatus isfurther configured to blow an inert gas and heat the chamber beforeadding the composition comprising the reactant. In yet another aspect,the chamber is part of a coin-shaped reactor in a radio-synthesis chip.In a different aspect, the electrodes are located in or on at least oneof a floor, a ceiling, and a side of the chamber or combinationsthereof, while in another aspect, the electrodes are located in achannel in fluid communication with the chamber.

In another aspect of the apparatus, the electrodes are non-metalelectrodes. In a different aspect, the electrodes are made of a materialselected from the group consisting of graphite, a composite graphite,and silicon and combinations thereof. In yet another aspect, theelectrodes are graphite polymer electrodes. According to another aspect,the polymer is selected from the group consisting of a DCPD, apolyethylene, and a glass, and in yet a different aspect, the electrodesare metal electrodes. In another aspect, the electrodes are covered witha protective coating, and according to a different aspect, at least oneof the first and the second electrodes is configured as an on-chipfeature or as an in-reactor feature. In one aspect, the electrochemicaltrapping is carried out in one or more passes, while in a differentaspect, the electrochemical releasing is carried out in accordance withone or more reversals of a voltage bias.

In one aspect of the apparatus, the trapping, the releasing and theradiolabeled compound formation are carried out within the samemicroreactor. In another aspect of the apparatus, the radiochemicallabeling yield of at least 55% is produced. In certain variations, theyield is 55%, 65%, 75%, 85%, 95% or 99%. In another variation, theradioactive isotope is released into a non-aqueous solution. In anothervariation, the non-aqueous solution is an organic solution, and thereaction to form the radiolabeled compound is a substitution reaction.In a particular variation, the releasing is carried out simultaneouslywith the substitution reaction. In one variation, the reactant is in asolvent.

These and other advantages and features of various embodiments of thepresent invention, together with the organization and manner ofoperation thereof, will become apparent from the following detaileddescription when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described by referring to the attacheddrawings, in which:

FIG. 1 illustrates exemplary steps for synthesis of a radioactiveisotope using an ion exchange column;

FIG. 2 illustrates exemplary steps for synthesis of a radioactiveisotope in accordance with an embodiment of the present application;

FIG. 3(A) illustrates an exemplary apparatus used for electrochemicaltrapping and release in a vial in accordance with an embodiment of thepresent application;

FIG. 3(B) illustrates an exemplary apparatus used for on-chipelectrochemical trapping and release in accordance with an embodiment ofthe present application;

FIG. 4(A) illustrates a cross-sectional view of an exemplarytrap-release chip in accordance with an embodiment of the presentapplication;

FIG. 4(B) illustrates a top view of an exemplary coin-chamber apparatusin accordance with an embodiment of the present application;

FIG. 4(C) illustrates a top view of an exemplary channel-based apparatusin accordance with an embodiment of the present application;

FIG. 5(A) illustrates an exemplary coin-shaped microreactor apparatus inaccordance with an embodiment of the present application;

FIG. 5(B) illustrates a top view of the bottom section of the exemplaryapparatus of FIG. 5(A) in accordance with an embodiment of the presentapplication;

FIG. 6(A) illustrates a top view of an exemplary electrochemicaltrap-release channel apparatus in accordance with an embodiment of thepresent application;

FIG. 6(B) illustrates a bottom view of the exemplary apparatus of FIG.6(A) in accordance with an embodiment of the present application;

FIG. 7 illustrates a cross-sectional view of an exemplary trap-releasechip in accordance with an embodiment of the present application;

FIG. 8(A) illustrates a top and side view of an exemplaryelectrochemical trap-release chip apparatus in accordance with anembodiment of the present application; and

FIG. 8(B) illustrates a bottom and side view of the exemplary apparatusof FIG. 8(A) in accordance with an embodiment of the presentapplication.

DETAILED DESCRIPTION OF THE CERTAIN EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, details and descriptions are set forth in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these details anddescriptions.

A “microfluidic device” or “microfluidic chip” or “synthesis chip” or“chip” is a unit or device that permits the manipulation and transfer ofsmall amounts of liquid (e.g., microliters or nanoliters) into asubstrate comprising micro-channels and micro-compartments. The devicemay be configured to allow the manipulation of liquids, includingreagents and solvents, to be transferred or conveyed within the microchannels and reaction chamber using mechanical or non-mechanical pumps.The device may be constructed using micro-electromechanical fabricationmethods as known in the art. Alternatively, the devices can be machinedusing computer numerical control (CNC) techniques. Examples ofsubstrates for forming the device include glass, quartz, silicon,ceramics or polymer. Such polymers may include PMMA(polymethylmethacrylate), PC (polycarbonate), PDMS(polydimethylsiloxane), DCPD (polydicyclopentadiene), PEEK and the like.Such device may comprise columns, pumps, mixers, valves and the like.Generally, the microfluidic channels or tubes (sometimes referred to asmicro-channels or capillaries) have at least one cross-sectionaldimension (e.g., height, width, depth, diameter), which by the way ofexample, and not by limitation, may range from 1,000 μm to 10 μm. Themicro-channels make it possible to manipulate extremely small volumes ofliquid, for example on the order of nL to μL. The micro reactors mayalso comprise one or more reservoirs in fluid communication with one ormore of the micro-channels, each reservoir having, for example, a volumeof about 5 to about 1,000 μL.

The term “radioactive isotope” refers to isotopes exhibiting radioactivedecay (e.g., emitting positrons). Such isotopes are also referred to inthe art as radioisotopes or radionuclides. Radioactive isotopes or thecorrespond ions, such as the fluoride ion, are named herein usingvarious commonly used combinations of the name or symbol of the elementand its mass number and are used interchangeably (e.g., ¹⁸F, 18F,[F-18], fluorine-18). Exemplary radioactive isotopes include I-124,F-18, C-11, N-13, and O-15, which have half-lives of 4.2 days, 110minutes, 20 minutes, 10 minutes, and 2 minutes, respectively. In onevariation, the term FLT precursor may be used to refer to“N-dimethoxytrityl-5′-O-dimethoxytrityl-3′-O-nosyl-thymidine” (alsoknown as “BOC-BOC-Nosyl”).

“Column” means a device that may be used to separate, purify orconcentrate reactants or products. Such columns are well known in theart, and include, but are not limited to, ion exchange and affinitychromatography columns. A “flow channel” or “channel” means amicrofluidic channel through which a fluid, solution, or gas may flow.It is also a channel through which vacuum can be applied. By the way ofexample, and not by limitation, such channels may have a cross sectionof about 0.1 mm to about 1 mm. By way of example, and not by limitation,the flow channels of embodiments of the present application may alsohave a cross section dimension in the range of about 0.05 microns toabout 1,000 microns. The particular shape and size of the flow channelsdepend on the particular application required for the reaction process,including the desired throughput, and may be configured and sizedaccording to the desired application.

The term “electrochemical trapping” refers to of the process ofseparating charged ions from a solution by applying a voltage across apair of electrodes that are in contact with the solution, therebycausing some, or substantially all, of the charged ions to be depositedonto, accumulated on, or collected in the vicinity of one of theelectrodes. The term “electrochemical releasing” refers to the processof releasing the trapped ions that have been deposited onto, accumulatedon, or collected in the vicinity of one of the electrodes, by applying avoltage across the pair of electrodes that are in contact with asolution. The voltage applied to carry out the electrochemicalreleasing, may, for example, be in the opposite direction of the voltageapplied to effect the electrochemical trapping.

FIG. 1 outlines a series of exemplary steps involved in the synthesis ofF-18 using a microfluidic device, from taking F-18 from cyclotron targetwater to fluorination reaction in a coin-shaped reactor chip using anion exchange column. In Step 1, with valves 102 and 108 closed andvalves 104 and 106 open, target water is passed through the ion exchangecartridge 110 to trap the F-18 out of a dilute solution. In Step 2, withvalves 104 and 106 closed and valves 102 and 108 open, K₂CO₃ is releasedinto a concentrated solution that enters the reactor. After thatdelivery has taken place, the valve 108 controlling the F-18 inletcloses, and in Step 3 water evaporation takes place. This drying steprequires a significant amount of processing time because of the need tomove water vapor across a membrane. In Step 4, K222/MeCN solution isdelivered from channel 112. This procedure also requires a significantamount of processing time because of dead end filing. In Step 5 drying,solvents are evaporated, leaving behind a residue containing[F-18]KF/K222 complex. This drying step also consumes a significantamount of processing time because of the need to move solvent vaporsacross a membrane, and the need for complete dryness. In Step 6, theprecursor or reactant (such as mannose triflate) is delivered to thereactor through channel 116. This step is also time consuming because ofdead end filling. Finally, in Step 7, the fluorination reaction takesplace.

Even under the best performance conditions, the number of required steps(i.e., seven steps) result in a slow or lengthy process, and furthercreates many points of potential failure. Furthermore, all steps areslow since they involve flow resistance induced by either the need topass the solutions through one or more columns, or dead end filling ofthe reactor displacing gases across the membrane. In particular, theoperation illustrated in FIG. 1 also involves two evaporation steps,both of which are slow since the vapor has to be transported across themembrane. In the case of water evaporation, most membranes are readilysaturated by water vapors that blocks further gas passage, making itdifficult to complete the evaporation within any reasonable period oftime. This is the major single obstacle to efficient operation of chipsthat utilize membranes. Chips without membranes have been designed andtested. However, they face the risk of losing valuable materials intoexhaust lines. Even if such risk is mitigated, it is still criticallyimportant to remove even minimal traces of water in order to assureefficient radio fluorinations. In addition, both types of devicesrequire heating during evaporation steps, which may easily causedegradation of phase transfer reagents, such as Kryptofix2.2.2.

In a particular aspect, water evaporation can be avoided altogether ifF-18 can be trapped out of target water and released into dry MeCNsolution in a concentrated manner. Such operation can be made possibleby electrochemical trapping and release. As reported by Hamacher et.al., F-18 can be extracted from a reservoir of target water onto agraphite positive electrode, where Platinum is used as the negativeelectrode. It can be released into ion-rich organic solution byreversing the bias. However, these systems cannot be adapted for usewith a batch microfluidic device for a variety of reasons. For example,the volume incompatibilities (e.g., 2.5 mL versus 50 uL) prevent the useof conventional trapping and/or release techniques in microfluidicdevices. Furthermore, since such techniques only work with standingsolutions and cannot be used to trap F-18 out of a moving solution, itis not possible to simply reduce the size of such devices. On the otherhand, a microfluidics approach, in accordance with the variousembodiments of the present application, allows the distance between theelectrodes to be made very small both on the absolute scale (e.g., tensto hundreds of microns) and on relative scale (i.e., compared to pathlength of the fluid). These features allow very efficient trapping ofF-18 out of a rapidly moving solution. For instance, the trapping from amoving solution, in accordance with exemplary techniques and devices ofthe present invention, may be carried out in less than one minute, asopposed to a five-minute trapping time that is typical for theconventional systems. Additionally, the various embodiments of thepresent invention allow reactions to take place in much moreconcentrated solutions, resulting in higher yields and shorter reactiontimes. According to other features of the various methods and apparatusof the present invention, any F-18 that was not initially trapped, maybe passed through the microfluidic device one or more times in order toallow trapping of additional F-18. This multiple-pass and/orrecirculation capability enables 100% trapping of F-18. Additionally,example embodiments of the microfluidic methods, systems and apparatusof the present application, enable a precise temperature control over awide range of temperatures, which is crucial for most radiosynthesisreactions. An example device constructed in accordance with theembodiments of the present application has demonstrated the capabilityfor trapping high percentages of F-18 out of various volumes of targetwater (e.g., 100 μL, 500 μL, 1 mL, 2 mL, 5 mL, 10 mL) in severalseconds. These results are already faster than the ion exchangecartridge trapping approach.

FIG. 2 illustrates a series of exemplary steps for electrochemicaltrapping and release of F-18 in a fully operational synthesis chip inaccordance with an embodiment of the present application. As illustratedin FIG. 2, both a positive electrode 202 and a negative electrode 204are placed within a reactor 200. In Step 1, electrochemical trapping ofF-18 on the inner surface or floor of the reactor 200 takes place. Step1 may be carried out as a fast unobstructed flow-through of dilute ¹⁸F⁻in H₂ ¹⁸O, followed by blowing N₂ while heating to dry the trappedfluoride. As the dilute solution of F-18 flows through the reactor, F-18gets trapped efficiently on the high surface area of the positiveelectrode 202. Upon passage of target water, the reactor 200 can beflushed with N₂ for drying purposes. If the dryness is not achieved to adesired level, the reactor 200 can be flushed or rinsed, for example, byMeCN, to remove the residual moisture, thus expediting the completion ofthis step and avoiding heating altogether when necessary. In Step 2, thereactor 200 is filled with the solution. In Step 3, electrochemicalrelease of F-18 takes place.

As the reactor 200 is filled with, for example, K₂CO₃/K222/mannosetriflate/MeCN solution, it has sufficient ionic strength for the releaseof F-18 upon reversing the bias. Since F-18 gets released into thetriflate solution it engages in reaction immediately. The releaseprocedure, however, does not have to be immediate. The release can becontrolled to be completed within the time period allowed for thefluorination, thus maximizing its yield. On the other hand, the overallprocess is expedited since the fluorination reaction is not postponeduntil the end of release and [F-18] fluoride transfer. As evident fromthe comparison of FIGS. 1 and 2 in the presently described process, fiverelatively slow steps may be replaced by one fast flow-through step,which involves only one dead-end filling process. Placing bothelectrodes (i.e., the positive electrode 202 and the negative electrode204) inside the reactor 200 generates two more advantages: (a) iteliminates the process for moving the concentrated F-18 from onecompartment to another, and (b) it eliminates extra valves necessary forcolumn operation. Note that the procedures involving F-18 transport areassociated with noticeable radioactivity losses when very small volumesare involved. This loss is partly due to competing side reactions withsystem components that are exposed to F-18 before contacting with thetriflate. In addition, varying percentages of F-18 may be inevitablylost in transit between the trap/release device and the synthesis vesselor device, if these entities are separate. With the speed of operationbeing one of the most critical issues in radiosynthesis, reducing thenumber of steps from seven to three, and eliminating several inefficientor high risk steps, leads to a dramatic improvement in reducing theprocess cycle time, radiochemical yield of the desired product androbustness of the chip operation. Experimental results have confirmedyields of at least 55%. Some exemplary yields obtained from theexperimental results include 10%, 40%, 55%, 65%, 75%, 85%, 95% and 99%.

In an alternative embodiment, an electrochemical trapping and releasedevice may be coupled with the reactor but not as part of the reactionchamber itself. Although this arrangement involves the conveyance ortransfer of F-18 to the reaction chamber, the advantage of release intoan organic solution still remains viable, and the electrodes are notsubject to heating that takes place during the reaction stages insidethe reaction chamber. Meanwhile, the distance between the trap/releaseunit and the reactor placed within the same chip is minimal andtherefore losses of F-18 in transit or during a transfer process is alsominimized.

FIG. 3(A) illustrates an example vial containing target water that isused for evaluation of electrodes made from different materials for thetrapping/release applications in accordance with various embodiments ofthe present application. FIG. 3(B) illustrates an example microfluidicchip that is implemented with trapping and release capabilities inaccordance with various embodiments of the present application. Both thevial and the chip of FIGS. 3(A) and 3(B) are example embodiments oftrap-release devices that may be implemented in accordance with thevarious embodiments of the present application. The following providesan exemplary set of test results for two different sets of electrodes:

-   -   Copper electrodes may provide up to 75% trapping (500V, and 5        min), up to 79% release into 0.5M KHCO₃ solution (500V, and        reverse bias pulsing). Some F-18 may be released into pure        water, and significant copper contamination of solution may        occur.    -   Graphite and graphite/DCPD composite electrodes may provide up        to 97% trapping, up to 96% release into 0.5M KHCO₃ solution. No        solution contamination may occur. Graphite/DCPD can be        molded/machined into very complex and precise shapes.

Experimental results indicate that copper fluorides are significantlyless reactive and are difficult to solubilize in organic solvents usingKryptofix2.2.2. Graphite is inert in this regard but is fragile, whichmakes machining and molding of the electrodes difficult. Furthermore, itmay not be suitable for exposure to high pressures. In accordance withan example embodiment of the present application, these deficiencies maybe overcome by using a composite material comprised of graphite and apolymer, such as polydicyclopentadiene (DCPD), as electrode material.For example, a composite graphite and DCPD material exhibitsconductivity that is comparable to that of pure graphite. When theelectrodes are fabricated using such composite material, they producetrapping and release efficiencies that are comparable to those of puregraphite electrodes of the same size and shape. Other exemplary materialwhich may be used in construction of composite electrodes include, butare not limited to, graphite blends with glass, quartz or other polymermaterial such as PMMA (polymethylmethacrylate), PC (polycarbonate), PDMS(polydimethylsiloxane), PEEK and the like. Accordingly, the electrodesof the various embodiments of the present application, may beadvantageously fabricated using such composite material since they canbe easily machined and molded, are thermally and chemically resistant,and are very tough. See, for example, U.S. Pat. No. 7,339,006, thedisclosure of which is incorporated herein by reference in its entirety.

Two different trapping processes may be used to effect the trapping andrelease of F-18. In one embodiment, bare electrodes may drive a currentthrough the solution. This approach relies on ¹⁸F⁻ being attracted tothe positive electrode, where it gets attached to the electrode formingionic bonds. Using this method, and given enough time, substantially allfluoride may be taken out of the solution since there is no equilibriumto maintain and no repulsion. When the bias is reversed, adsorbed[F-18]F⁻ is released into the solution. Again, given sufficient amountof time, substantially all F-18 may be released. Experimental resultshave confirmed proper release of suitable F-18, and its reactivitytowards mannose triflate. For example, vial experiments havedemonstrated trap and release of F-18, and successful reaction withacetylated mannose triflate, producing, for example, up to 60% yields ofacetylated 2-deoxy-2-fluoroglucose. In these experiments, Graphite/DCPDcomposite electrodes were used to trap F-18 from target water, followedby drying and immersion into mannose triflate/K₂CO₃/K222/MeCN solutionand heating (in a vial), resulting in 55-60% fluorination yield (basedon released fluoride). This approach has been further confirmedexperimentally using on-chip implementations.

In another exemplified embodiment of the present application, thetrapping and release of F-18 may be carried out using insulatedelectrodes so that F-18 is attracted to the positive electrode by theelectric field alone. This approach is advantageously designed to assurethat F-18 does not undergo any transformations and/or reactions betweenthe trapping and the release stages, and that it does not pick up anycounter ions (such as Cu²⁺) (or to minimize any such transformations orreactions) that may hinder fluorination reactions. Using insulatedelectrodes and the electric field, ¹⁸F⁻ is attracted towards thepositive electrode and is held on its surface electrostatically untilthe bias is reversed. This method involves high concentrationaggregation of ¹⁸F⁻ on the positive electrode surface. Concentration ofnegative charges may start to repel further fluoride adsorption at acertain point when equilibrium is reached since the attraction is muchweaker than with bare electrodes. The adsorption of F-18, however, maybe improved by increasing the surface area of the positive electrode.This approach has been demonstrated experimentally using both test vialsand on-chip implementations.

FIG. 4(A) illustrates a cross-sectional view of an example microfluidicchip for implementing a trap/release procedure in accordance with anembodiment of the present application. The example chip of FIG. 4(A) isspecially designed to allow evaluation of the trapping efficiencyseparately from other variables, without performing subsequentreactions. In addition, it allows a wide range and variations of shapeand volume of the trapping feature to be studied. As illustrated in FIG.4(A), the positive electrode 406 is positioned in the floor of trappingchamber/channel 402 and the negative electrode 404 is positioned in theceiling of the trapping chamber/channel 402. FIG. 4(A) also illustratesthe loading channel 412, the insulating/sealing gasket 408 that is usedto ensure proper sealing between the top and bottom sections of thechip, and the screws 410 that are used to firmly hold the top and bottomsections of the chip together. Once on-chip trapping is optimized, thefeasibility of an in-reactor trap integration may be evaluated. Theexemplary trap chip design that is presented in FIG. 4(A) maximizes theexposure of electrodes to the solution while keeping them insulated fromone another. In addition, the chip is sufficiently sealed to preventleaks. This design has been implemented in a chip, such as the exemplarydevice that is illustrated in FIG. 3(B). In one exemplary embodiment,both electrodes are constructed using aluminum, with the bottomelectrode being a machined block and the top electrode being foilpressed between DCPD and the soft gasket. The same architecture may beimplemented to make devices with coin-shaped chambers, as well as longchannel trap devices. FIG. 4(B) illustrates a top view of a coin-chamberbased device, and FIG. 4(C) illustrates a top view of a channel baseddevice.

In another example embodiment, both electrodes may be constructed usinga graphite-DCPD blend. FIGS. 5(A) and 5(B) illustrate one such exemplarychip with a coin-shaped reactor 502 that has been successfullyfabricated and tested. This configuration is comprised of two sections:a top section 504 and a bottom section 506 that are firmly held togetherusing a plurality of screws 508 and a thin gasket around the reactor. Acoin-shaped reactor 502 is located within the center of the chipassembly, and graphite-DCPD electrodes 510 are placed in the floor andceiling of the reactor. As depicted in FIG. 5(A), the two electrodes 510protrude from the top and the bottom sections of the assembled chip. InFIG. 5(B), the bottom section of the chip 506 is illustrated, along withliquid ports 512, a reaction chamber 502 (e.g., 250 μm deep), and theelectrode 510 that is connected to the floor of the reaction chamber502. The same architecture may be implemented to make devices with along channel trap, such as the one illustrated in FIGS. 6(A) and 6(B).FIG. 6(A) illustrates the top view of an electrochemical trap with a4-cm channel, with liquid ports 604, electrode leads 602 and a valveactuator 606 clearly visible. In FIG. 6(B), the bottom view of the samedevice is depicted, with the embedded graphite electrodes 608 clearlyvisible.

As compared to coin-shaped trap chips, the chips with long channel trapconfigurations, such as the ones illustrated in FIGS. 4(C), 6(A) and6(B), have the advantage of having a larger surface-area-to-volumeratios, which allow the solution to remain in contact with theelectrodes for a longer period of time, thus leading to trappingefficiencies that are far superior to those of coin chambers. On theother hand, coin-shaped chips have the following advantages: (a) theirevaluation allows easy transformation to in-reactor trapping, (b) suchtest devices can be easily fabricated using existing parts, and (c) theydo not involve transferring of concentrated F-18 solutions.Additionally, if single-pass trapping is not efficient enough, the F-18solution can be passed through the trap multiple times until all F-18has been extracted. Similarly, the efficiency of release may be improvedby reversing the bias several times in order to release all F-18, eventhat portion that is adsorbed onto the new positive electrode (i.e., thenegative electrode during trapping). As noted earlier, in both the longchannel trap and coin-shaped designs metal electrodes may be replaced bya composite material such as graphite/DCPD.

In accordance with another example embodiment, in certain configurationswhere the coin-reactor does not demonstrate the desired efficiency, thetrapping device may be separated from the radio-synthesis micro-reactoror the entire chip. The advantage of such an arrangement is that thereactor operation is not jeopardized by the integration of electrodes,and that of the trap is not jeopardized by high temperatures and variousreagents used in the reaction chamber. However, in this configuration,F-18 may have to be released with extremely high efficiency to make itstransport from one place to the next feasible. In another embodiment, inorder to increase the trapping efficiency in a coin reactor or achannel, multiple passes of the same F-18 solution may be performed.This technique may further minimize the path length and allow easierintegration of electrodes. In yet another embodiment, electrochemicaltrapping and release may be carried out from one solution into another,where the two solutions form a laminar flow in a microchannel.

FIG. 7 illustrates an alternative design for an in-reactor trappingprocess in accordance with an example embodiment of the presentapplication. As illustrated in FIG. 7, one electrode, for example thepositive electrode 706, as well as the other electrode, for example, thenegative electrode 704, are positioned in the floor of the trappingchamber/reactor 702, with the positive electrode 706 having asignificantly larger surface area than the negative electrode 704. FIG.7 also illustrates the loading channel 712 and the insulating/sealinggasket 708 to ensure proper sealing between the top and bottom sectionsof the chip. The positive electrode 706 may be a block similar to theconfiguration shown in FIG. 4(A), but the negative electrode 704 may beconstructed by drilling a hole in the positive electrode block 706 thatis filled with, for example, a DCPD-insulated negative electrode wire.This configuration allows the current to be still driven through thesolution while clearing the top surface of the reactor forimplementation of functional vents 710. In a membrane-free arrangement,this configuration is still advantageous since it allows the vents to belocated in the ceiling, where they do not touch the liquid within thereaction chamber. In addition, the transparent reactor ceiling allowsmonitoring of the reaction chamber and progress tracking. In anin-reactor trapping process, this design allows F-18 to reactimmediately upon release, and allows residual F-18 to be released afterthe reaction has started. FIG. 8 illustrates an exemplary trap with a5-mm channel that has been successfully fabricated and tested inaccordance with design principles that are depicted in FIG. 7. FIG. 8(A)illustrates a top and side view of the chip with a liquid port 802,electrode leads 804 and vent ports 806 clearly visible. FIG. 8(B)illustrates a bottom-and-side view of the same chip with electrode leads804 and vent ports 806 clearly visible. It should be noted that whileFIG. 4 and FIG. 7 illustrate two exemplary electrode configurations,other electrode geometries may be implemented in accordance with variousembodiments of the present application. For example, both or eitherelectrodes may be placed within any one of the following elements:floor, ceiling, and sides of the reactor, as well as the channelsleading up to the reactor.

Table 1 illustrates the various exemplary results obtained fromevaluating F-18 trapping and release using vial experiments.

TABLE 1 Exemplary Trapping and Release Results Using Vial ExperimentsElectrode Material Test Conditions Results Insulate Copper In-solution;No voltage applied 0.2% trapping by absorption Applied 100 Volts for 5min 1.2% trapping Applied 500 Volts for 5 min 1.1% trapping Bare CopperApplied 100 Volts for 5 min 10% trapping Applied 500 Volts for 5 min 75%trapping Reverse bias to release into 1.7% release MeCN K222 solution,500 Volts for 5 min Pulsing voltage to release 79% release into KHCO₃solution Insulated Graphite Applied 500 Volts for 5 min 2.3% trappingBare Graphite Applied 500 Volts for 5 min 54% trapping Reverse bias torelease into No release; K₂CO₃ aqueous solution too conductive, powershuts off Reverse bias to release into 51% release pure water with 500Volts Pulsing voltage; release into 96% release 0.5M KHCO₃ solutionInsulated Applied 500 Volts for 5 min 1.06% trapping Graphite/DCPD BareApplied 500 Volts for 5 min 97% trapping Graphite/DCPD

Chemistry validation was conducted as follows: trapping was carried outusing 100V for 5 min using Graphite/DCPD electrode, followed by dryingwith hot air and MeCN, followed by release into K222/K₂CO₃/MeCNsolution, and followed by addition of acetylated mannose triflate (uponremoval of electrodes). The results indicate 55-60% radiochemical yieldof acetylated 2-deoxy-2-fluoroglucose as calculated from releasedfluoride.

Table 2 illustrates the various exemplary results obtained fromevaluating F-18 trapping and release using chip experiments.

TABLE 2 Exemplary Trapping and Release Results Using Chip ExperimentsElectrode Material Test Conditions Results Insulated 30 μm gasketcovering the top 0-0.2% trapping Electrodes electrode; 2-Volt operationBare graphite 100 V trapping, single pass 20% Bare Aluminum 10 μL/secflowing solution with 92% trapping 200-Volt operation

In addition, graphite electrodes with (a) 5 mm channel, (b) 4 cmchannel, and (c) coin-reactor with full top and bottom surfaces havebeen successfully fabricated and tested.

All references cited herein are incorporated by reference as if each hadbeen individually incorporated by reference in its entirety. Indescribing embodiments of the present invention, specific terminology isemployed for the sake of clarity. However, the invention is not intendedto be limited to the specific terminology so selected. Nothing in thisspecification should be considered as limiting the scope of the presentinvention. All examples presented are representative and non-limiting.For instance, while one exemplary radioactive isotope may have beendescribed in connection with the various embodiments of the presentapplication, it is understood that other radioactive isotopes, as wellas non-radioactive material, may be used in connection with the variousembodiments of the present application without departing from the scopeof the present application. The above-described embodiments may bemodified or varied, without departing from the invention, as appreciatedby those skilled in the art in light of the above teachings. It istherefore to be understood that, within the scope of the claims andtheir equivalents, the invention may be practiced otherwise than asspecifically described.

1. A method for the synthesis of a radiolabeled compound comprising aradioactive isotope using a microfluidic device, the method comprising:introducing a composition comprising a radioactive isotope to themicrofluidic device; electrochemically trapping the radioactive isotopeusing an electrode; adding a composition comprising a reactant to thereactor; electrochemically releasing the radioactive isotope from theelectrode; and contacting the reactant with the radioactive isotope toform the radiolabeled compound.
 2. The method of claim 1, wherein theradioactive isotope is F-18.
 3. The method of claim 1, wherein thereactant comprises mannose triflate.
 4. The method of claim 3, whereinthe reactant isN-dimethoxytrityl-5′-O-dimethoxytrityl-3′-O-nosyl-thymidine and theradiolabeled compound is FLT.
 5. The method of claim 2, wherein a stepof blowing an inert gas and a heating of the reactor is performed to drythe trapped F-18 before adding the composition comprising the reactantto the reactor.
 6. The method of claim 1, wherein the reactor is acoin-shaped reactor in a radio-synthesis chip.
 7. The method of claim 1,wherein the trapping and releasing is carried out by one or moreelectrodes.
 8. The method of claim 7, wherein the electrodes are locatedin or on at least one of a floor, a ceiling, and a side of the reactoror combinations thereof.
 9. The method of claim 7, wherein theelectrodes are located in a channel in fluid communication with thereactor.
 10. The method of claim 7, wherein the electrodes are non-metalelectrodes.
 11. The method of claim 7, wherein the electrodes are madeof a material selected from the group consisting of a graphite, acomposite graphite, and silicon and combinations thereof.
 12. The methodof claim 11, wherein the electrodes are graphite polymer electrodes. 13.The method of claim 12, wherein the polymer is selected from the groupconsisting of a DCPD, a polyethylene, and a glass.
 14. The method ofclaim 7, where the electrodes are metal electrodes.
 15. The method ofclaim 14, wherein the electrodes are covered with a protective coating.16. The method of claim 1, wherein at least one of the electrochemicaltrapping and the releasing is carried out in accordance with an on-chipfeature.
 17. The method of claim 1, wherein at least one of theelectrochemical trapping and the releasing is carried out in accordancewith an in-reactor feature.
 18. The method of claim 1, wherein thetrapping, the releasing and the radiolabeled compound formation arecarried out within the same microreactor.
 19. The method of claim 1,wherein a radiochemical labeling yield of at least 55% is produced. 20.The method of claim 19, wherein the yield is 55%, 65%, 75%, 85%, 95% or99%.
 21. The method of claim 1, wherein the radioactive isotope isreleased into a non-aqueous solution.
 22. The method of claim 21,wherein the non-aqueous solution is an organic solution.
 23. The methodof claim 1, wherein the reaction to form the radiolabeled compound is asubstitution reaction.
 24. The method of claim 23, wherein the releasingis carried out simultaneously with the substitution reaction.
 25. Themethod of claim 1, wherein the reactant is in a solvent.
 26. The methodof claim 1, wherein the electrochemical trapping is carried out in oneor more passes.
 27. The method of claim 1, wherein the electrochemicalreleasing is carried out in accordance with one or more reversals of avoltage bias.
 28. A method for the synthesis of a radiolabeled compoundusing a microfluidic trap-release device, the method comprising:introducing a composition comprising a radioactive isotope to thedevice; electrochemically trapping of the radioactive isotope; adding acomposition comprising a reactant to the device; and electrochemicallyreleasing the radioactive isotope into the trap-release device.
 29. Themethod of claim 28, wherein the trap-release device is a radiochemicalmicroreactor.
 30. A microfluidic radiosynthesis apparatus, comprising: afirst electrode configured to electrochemically trap a radioactiveisotope; a chamber; and a second electrode configured toelectrochemically release the radioactive isotope into the chamber. 31.The apparatus of claim 30, wherein the apparatus is further configuredfor preparing a radiolabeled compound by performing a reaction of areactant with the radioactive isotope.
 32. The apparatus of claim 30,wherein the radioactive isotope is F-18.
 33. The apparatus of claim 30,wherein the chamber is filled with a composition comprising a reactant.34. The apparatus of claim 33, wherein the reactant comprises mannosetriflate.
 35. The apparatus of claim 34, wherein the reactant isN-dimethoxytrityl-5′-O-dimethoxytrityl-3′-O-nosyl-thymidine and theradiolabeled compound is FLT.
 36. The apparatus of claim 33, furtherconfigured to blow an inert gas and heat the chamber before adding thecomposition comprising the reactant.
 37. The apparatus of claim 30,wherein the chamber is part of a coin-shaped reactor in aradio-synthesis chip.
 38. The apparatus of claim 30, wherein theelectrodes are located in or on at least one of a floor, a ceiling, anda side of the chamber or combinations thereof.
 39. The apparatus ofclaim 30, wherein the electrodes are located in a channel in fluidcommunication with the chamber.
 40. The apparatus of claim 30, whereinthe electrodes are non-metal electrodes.
 41. The apparatus of claim 30,wherein the electrodes are made of a material selected from the groupconsisting of graphite, a composite graphite, and silicon andcombinations thereof.
 42. The apparatus of claim 41, wherein theelectrodes are graphite polymer electrodes.
 43. The apparatus of claim42, wherein the polymer is selected from the group consisting of a DCPD,a polyethylene and a glass.
 44. The apparatus of claim 30, where theelectrodes are metal electrodes.
 45. The apparatus of claim 44, whereinthe electrodes are covered with a protective coating.
 46. The apparatusof claim 30, wherein at least one of the first and the second electrodesis configured as an on-chip feature or as an in-reactor feature.
 47. Theapparatus of claim 30, wherein the electrochemical trapping is carriedout in one or more passes.
 48. The apparatus of claim 30, wherein theelectrochemical releasing is carried out in accordance with one or morereversals of a voltage bias.